CN101116267B - Optical input interruption detection device - Google Patents

Abstract

The invention provides an optical input interruption detection device. The present invention relates to an optical transmission device, and particularly to an optical input interruption detection device for detecting an input interruption of an optical signal received by a terminal station, a relay station, or the like in the order of SD and SF in synchronous optical communication networks such as SDH and SONET. The optical input interruption detection device includes: an optical input unit for outputting received optical power drop information and an LOS alarm based on the measurement of the received optical power of the optical input signal; a synchronizing part for extracting the synchronous clock contained in the optical input signal and outputting LOL alarm when the optical input signal is out of step; and an optical input interruption detecting unit for determining whether or not the received optical power drop information is present, and if the information is present, validating the LOS alarm by the output of the LOL alarm, and if the information is absent, immediately validating the LOS alarm, and detecting an optical input interruption based on the validated LOS alarm.

Description

Optical input interruption detection device

technical field

The present invention relates to an optical transmission device, in particular to a device for detecting optical signals received by terminal stations and relay stations in synchronous optical communication networks such as SDH (Synchronous Digital Hierarchy) and SONET (Synchronous Optical Network, synchronous optical network) Optical input loss detection means for loss-of-signal.

Background technique

Terminal stations and relay stations in a synchronous optical communication network have a device that monitors the input level of an optical signal received from an opposing station, calculates an error rate of received data, etc., and detects abnormalities such as interruption of optical input. When abnormalities such as optical input interruption (LOS: Loss of Signal, loss of signal) are detected, the terminal station and the relay station switch the communication path from the working system to the protection system in order to maintain the normal communication state, and send information to the operator terminal in the station and the downlink The first-level terminal station, etc. outputs an alarm indicating that the optical input is interrupted.

FIG. 1 shows a configuration example of a conventional optical input interruption detection device of an optical transmission device.

In Fig. 1, the optical signal sent by the opposite station is input into the optical transceiver 1 of the station, and the data after optical/electrical (O/E: Optical/Electrical) conversion is input into the clock/data recovery unit (CDR: Clock & Data Recovery) 2.

The optical transceiver 1 includes an unillustrated optical output constant control unit and the like, and when a signal below a predetermined optical input level is detected using an optical AGC control signal or the like, an output corresponding to a severe failure (SF: Signal ) is output to the data processing unit 3. Failure) optical input interruption (LOS) alarm.

The clock/data recovery unit 2 extracts a clock component included in an input data signal, recovers a reception clock, and samples input data using the extracted clock, thereby restoring reception data from the opposing station. The data and the clock recovered by the clock/data recovery unit 2 are output to the data processing unit 3 .

The data processing unit 3 performs decoding processing of the received data to restore the transmission source data. At this time, the bit error rate (BER: Bit Error Rate) of the received data is calculated to determine the degree of degradation of the communication line. If the BER is above a predetermined value, it is determined that the signal degradation corresponds to a minor failure compared to SF ( SD: Signal Degrade), and record the information.

In addition, when an LOS alarm is detected, the data processing unit 3 outputs consecutive data values of "0" to the next stage in order to perform inter-system switching from the working system to the protection system and to perform line abnormality alarm processing.

Another configuration example of a conventional light input interruption detection device is shown in FIG. 2 .

In this example, instead of the LOS alarm from the optical transceiver 1 of FIG. 1, the asynchronous (self-propelled) state of the output of the PLL (Phase Locked loop, phase-locked loop) circuit, etc. present in the clock/data recovery unit 2 is displayed. The out-of-synchronization (LOL: Loss of Lock) alarm corresponds to a serious fault (SF), and is output to the data processing unit 3. Others are the same as the structure in Fig. 1. In addition, here, in the clock/data recovery unit 2, a commercially available CDR device that satisfies the common specifications of the MSA (Multi Source Agreement) of the SDH-related private sector is used.

In this example, if a LOL alarm is detected, in order to switch from the working system to the protection system between systems and to perform alarm processing for line abnormalities, the data processing part 3 outputs data with a continuous data value of "0" to the next level. (Refer to Patent Document 2).

Patent Document 1: Japanese Patent Laid-Open No. 2001-339347

Patent Document 2: Japanese Patent Application Laid-Open No. 7-95156

In the conventional configuration shown in FIG. 1 , the optical transceiver 1 outputs an LOS alarm based on the received light level irrespective of the signal error (BER) calculated by the data processing unit 3, so that the light fault SD and the severe fault cannot be determined. The sequence of SFs detects failure conditions. Usually, the LOS in Fig. 1 is set to the same failure level as SF, for example, SD is set to BER IE-6(10 ^-6 ), and LOS(SF) is set to BER IE-4(10 ^-4 ) about.

As a result, a line fault of the class SD that should have been detected as a continuation of use in the conventional system may be detected as a serious line fault SF. In addition, although station maintenance personnel and sales parties perform BER analysis before or at the time of failure to find out the cause of the failure, this analysis cannot be performed in the above case, so there is a possibility that failure monitoring using BER is not effective. problem of functioning.

In addition, in the conventional structure of FIG. 2, there is the following problem: Although the characteristics of the CDR equipment sold on the market are used to output the LOL alarm of out-of-synchronization around BER IE-4, which is a serious failure (SF), the PLL, etc. Due to the limitations of the circuit structure, the LOL detection speed, that is, the time from the interruption of the optical input to the detection of out-of-synchronization does not meet the SF detection time within 100 μS stipulated in the standard GR-253.

For this reason, in addition to the detection function of the above-mentioned LOL, the following method is also used: when the optical input level drops below a predetermined level, the characteristic of the conventional optical transceiver 1 outputting a continuous signal with a data value of "0" , when the clock/data recovery unit 2 detects the continuous data value "0", it immediately outputs a LOL alarm.

However, the optical transceiver 1 in recent years has a structure in which an amplifier associated with constant control of the optical output is built in in order to improve the receiving sensitivity and expand the receiving range, and even if the optical signal is a signal with a low noise level, it outputs an amplified signal containing noise. after the data. Therefore, the above-mentioned conventional method (detection of consecutive 0s) cannot be used in the next-stage clock/data recovery unit 2 .

Contents of the invention

Therefore, the object of the present invention is to, in view of the above-mentioned problems, provide a kind of optical input interruption detecting device, it monitors the input level of the optical signal received, when the optical input level is above a predetermined level, then detects a serious failure immediately ( SF), on the contrary, when the optical input level is below the predetermined level, the detection of slight fault (SD) is prioritized, and after the detection, by allowing the detection of severe fault (SF), so that the simultaneous realization of the optical input level based Early detection of SF and ensure detection sequence from SD to SF.

According to the present invention, there is provided an optical input interruption detection device, the optical input interruption detection device includes: an optical input part, which is based on the measurement of the received optical power of the optical input signal, and the optical input part measures the received optical power of the optical input signal Perform measurement, output received optical power drop information when the received optical power is below the received optical power drop threshold, and output an optical input interrupt alarm when the received optical power is below the optical input interrupt alarm threshold, wherein the optical input interrupt alarm threshold is less than the received optical power drop threshold Optical power drop threshold; synchronization section, which extracts the synchronous clock included in the above-mentioned optical input signal, and outputs LOL alarm when out of sync; optical input interruption detection section, which determines whether there is any above-mentioned received optical power drop information, In the case of optical power drop information, the above-mentioned LOS alarm is validated according to the output of the above-mentioned LOL alarm, and in the case of the absence of the above-mentioned received optical power drop information, the above-mentioned LOS alarm is immediately validated, and the optical input interruption is detected by the valid LOS alarm ; A bit error rate measurement unit, the bit error rate measurement unit measures the bit error rate of the received data recovered using the above-mentioned synchronous clock, and when the measured bit error rate is within a predetermined bit When the bit error rate exceeds the value, it is judged as a fault state of the minor fault level.

The optical input interruption detection unit considers the LOL alarm output as an active LOS alarm instead of enabling the LOS alarm based on the LOL alarm output when the received optical power drop information is present.

The BER value of the SD-level fault state is smaller than the BER value of the LOS-level or LOL-level fault state. In addition, the BER value of the failure state of the above-mentioned LOS level or the above-mentioned LOL level is substantially equal to the BER value of the failure state of the SF level. Furthermore, the received optical power drop information is output every predetermined cycle, or the received optical power drop information is output after a predetermined delay time has elapsed from the time when the information was acquired.

According to the present invention, in the receiving state with a sufficiently large optical input level (there is no received optical power drop information), the reason why the optical input interruption (LOS) is detected is only due to serious faults (SF) such as device failure and line disconnection. , Therefore, at this time, LOS is detected immediately so as to satisfy the SF detection time within 100 μS of the standard GR-253.

On the other hand, in a state where the optical input level is lower than the minimum receiving level (received optical power drop information exists), usually, the received light level from the opposite station is sufficiently higher than the minimum received level of the receiving station , it can be assumed that signal interruptions are gradually occurring due to time-dependent deterioration of in-station devices and inter-station transmission lines, changes in ambient temperature, and the like. Therefore, in the state where the optical input signal level drops, the BER is measured during the continuous use of the system to detect a slight failure (SD; BER IE-6) that can continue to be used in the system, and this SD detection is regarded as condition (after SD detection), further detection of severe faults after fault aggravation (LOL; BER IE-4).

Therefore, using the BER-based fault detection function, detailed fault analysis up to serious faults can be carried out, and the maintenance operation of the station and the entire system becomes extremely easy. In addition, for the above reasons, in the present invention, the above-mentioned conventional method (detection of consecutive 0s) is unnecessary, and a low-cost and efficient device design using a commercially available CDR device can be realized.

Description of drawings

FIG. 1 is a diagram showing a configuration example of a conventional light input interruption detection device.

FIG. 2 is a diagram showing another configuration example of a conventional light input interruption detection device.

Fig. 3 is a diagram showing a first embodiment of an optical input interruption detection device of the present invention.

FIG. 4 is a diagram showing an example of a control flow of a LOS control unit.

FIG. 5 is a diagram showing an example of a specific circuit configuration of an LOS control unit.

FIG. 6 is a diagram showing an example (1) of the operation timing chart in FIG. 3 .

FIG. 7 is a diagram showing an example (2) of the operation timing chart in FIG. 3 .

Fig. 8 is a diagram showing a second embodiment of the light input interruption detecting device of the present invention.

FIG. 9 is a diagram showing an example (1) of the operation timing chart in FIG. 8 .

FIG. 10 is a diagram showing an example (2) of the operation timing chart in FIG. 8 .

Detailed ways

Fig. 3 is a diagram showing a first embodiment of an optical input interruption detection device of the present invention.

In FIG. 3, the optical transceiver 1, the clock/time recovery unit (CDR) 2, and the data processing unit 3 are the same as those of the conventional example. Therefore, no further description is given here. In addition, due to MSA-based optical transceivers, recent optical transceivers 1 already have various monitoring functions and/or detection functions for optical output power, internal temperature, power supply voltage, and the like. In the present invention, the monitoring function of the received optical power or the alarm function of the received optical power are used for LOS detection.

In addition, in this example, the newly added LOS control unit 4 receives the received optical power drop information and the LOS alarm from the optical transceiver 1, and the LOL alarm from the clock/data recovery unit 2, and according to the received optical power drop information and the The LOL alarm controls the passage of the LOS alarm from the optical transceiver 1 to the data processing unit 3 . When the LOS warning is issued, the data processing unit 3 executes the same processing as in the conventional example of FIG. 1 .

In addition, the LOS control unit 4 can also output the LOS alarm from the optical transceiver 1 or the LOL alarm from the clock/data recovery unit 2 indicating a serious failure (BER IE-4) according to the received optical power drop information from the optical transceiver 1. Either of the two sides (refer to FIG. 5 described later). When the LOL warning is issued, the data processing unit 3 executes the same processing as in the conventional example of FIG. 2 .

An example of the control flow of the LOS control unit 4 is shown in FIG. 4 .

In this example, the LOS control unit 4 monitors received optical power drop information (received optical power drop warning in this example) from the optical transceiver 1, and determines its presence or absence (S01). When, for example, the received optical power value measured every predetermined period or its average value falls below the minimum guaranteed received optical power value, a received optical power drop warning is output.

When the receiving optical power drop warning is not detected (OFF), the LOS warning from the optical transceiver 1 is monitored to determine its presence or absence (S03). When the LOS alarm is detected (ON), it is output to the data processing unit 3 (S04). On the other hand, when the LOS alarm is not detected (OFF), it returns to the monitoring of the received optical power drop alarm (S01).

In this way, in the state where the received optical power drop warning is not detected (the received optical power is above the minimum received optical power value), the LOS control unit 4 outputs the input LOS warning to the information processing unit 3 as it is, thereby satisfying the 100 μS specified value.

On the other hand, when the received optical power drop warning is detected (ON), the LOL warning from the clock/data recovery unit 2 is monitored to determine its presence or absence (S02). When the LOL alarm is detected (ON), the LOS alarm input from the optical transceiver 1 is passed and output to the information processing unit 3 (S04). When the LOL alarm is not detected (OFF), return to the monitoring of the received optical power drop alarm (S01).

In this way, in the state in which the received optical power drop alarm is detected (the received optical power is below the minimum received optical power value), the LOS control unit 4 uses the detection of the LOL alarm from the clock/data recovery unit 2 as a condition (after LOL detection) to The information processing unit 3 outputs the input LOS warning. Thus, the order of occurrence of SD and LOS is observed.

FIG. 5 is a diagram showing an example of a specific circuit configuration of an LOS control unit.

In FIG. 5, in the inverter 41 of the LOS control section 4, the received light power drop alarm from the optical transceiver 1 is input, and the output of the inverter 41 is input to the "AND" (AND) circuit 42 of the next stage. Output and LOS warning from Optical Transceiver 1. Therefore, when the reception optical power drop warning is not detected (value "0"), the AND circuit 42 passes the LOS warning from the optical transceiver 1 as it is. On the contrary, when the received optical power drop alarm is detected (the value is “1”), the LOS alarm from the optical transceiver 1 is prohibited from passing through.

In addition, the received optical power drop warning from the optical transceiver 1 is input to one input of the AND circuit 43 , and the LOL warning from the clock/data recovery unit 2 is input to the other input. Therefore, the AND circuit 43 prohibits the passage of the LOL alarm from the clock/data recovery section 2 when the received optical power drop alarm is not detected (the value is “0”). Conversely, when the received optical power drop warning is detected (value "1"), the LOL warning from the clock/data recovery unit 2 is passed as it is.

As a result, either the LOS alarm from the optical transceiver 1 or the LOL alarm from the clock/data recovery unit 2 is output from the OR circuit 44 of the output stage according to the presence or absence of the received optical power drop alarm. Furthermore, in this example, because each failure level of LOS and LOL is equal to the failure level (BER IE-4) of SF, the output alarm in the figure is displayed with LOS alarm.

In this example, the received optical power is monitored through the received optical power drop alarm (or the monitoring signal of the received optical level) from the optical transceiver 1, when the received optical power is greater than or equal to the minimum received optical power guaranteed by the optical transmission device value, the LOS monitoring based on the received optical power of optical transceiver 1 is enabled, and when the received optical power is less than or equal to the minimum value of the received optical power, the LOS alarm based on the received optical power is disabled, and the monitoring comes from the clock/data recovery LOL warning for part 2.

As a result, within the range of received optical power guaranteed by the optical transmission device, LOS can be detected within 100 μs from the interruption of the optical input. In addition, when the received optical power falls below the guaranteed value, it can be considered that LOS detection is performed by the LOL alarm output after SD detection using BER, so that the failure sequence from SD to LOS can be followed.

6 and 7 show an example of an operation timing chart of the optical input interruption detection device of the present invention. Here, FIG. 6 shows an example of a situation where the received optical power is greater than the minimum received optical power value guaranteed by the optical input interruption device, and FIG. 7 shows that the received optical power is less than the minimum received optical power value guaranteed by the optical input interruption detection device. An example of the case of power values.

Fig. 6 shows that in the state where an optical signal with received optical power sufficiently large compared to the minimum received optical power shown in Fig. An example of operation when the power becomes 0. At this time, the difference between the received optical power value measured in a period of several mS to tens of mS or their average value and the minimum received optical power value (refer to the received optical power alarm threshold in (a) of FIG. 7 ) In comparison, the received optical power output from the optical transceiver 1 is output as a drop alarm. Therefore, the output is delayed in mS levels based on the aforementioned predetermined period from the interruption of the optical input ( FIG. 6( b )). Until the received optical power drop warning is output, the LOS control unit 4 determines this state as a state in which an optical signal having a received optical power greater than the minimum received optical power is input. In addition, it is also possible to delay the output by about 1 ms by adding, for example, a capacitive element to the output line (the input of 41 in FIG. 5 ) of the received light power drop warning, during which time the received light shown in FIG. 6(a) can be detected. Instantaneous changes in power, while reliably outputting an LOS alarm (refer to 42 in FIG. 5 ).

On the other hand, the LOS alarm output by the optical transceiver 1 is detected by simply comparing the LOS threshold (see FIG. 7( a )) of the optical input power and the received optical power. Therefore, the LOS alarm and the light input interruption are detected almost simultaneously as shown in Fig. 6(c). In addition, in this example, the LOL alarm from the clock/data recovery unit 2 shown in FIG. 6( d ) is ignored.

In this example where the received optical power is greater than the minimum received optical power, as shown in FIG. Receive it and start alert processing immediately. Therefore, as shown in the figure, if the LOS alarm is used, the prescribed SF detection time (T) of 100 μS can be fully satisfied.

Figure 7 shows that the optical input power gradually decreases due to the deterioration of inter-station devices and transmission lines over the years and changes in ambient temperature (Figure 7(a)), and the ratio of the optical input power to the received optical power alarm threshold and the received optical power An example of an action in the case of a lower LOS threshold. Here, the optical input signal with the received optical power greater than the received optical power alarm threshold can be received without error, but the optical input signal with the received optical power less than the LOS threshold of the received optical power cannot be received, and there is a received optical power alarm threshold and receiving The optical input signal with received optical power between the LOS threshold of optical power can be received at a BER level (SD) that can continue to be used in the existing system.

This example takes as an object an optical signal having an intermediate received optical power between the received optical power warning threshold and the received optical power LOS threshold at the start of the action. Therefore, as in the case of FIG. 6 , a severe fault (SF) which does not have to take intermediate received optical power into consideration due to line interruption or the like is excluded from the object of this example.

As shown in FIG. 7( b ), when the received optical power of the optical input signal is lower than the received optical power alarm threshold, a received optical power drop alarm is output. During the period from the detection time of the received optical power drop warning to at least detecting the LOL warning from the clock/data recovery unit 2, the LOS control unit 4 ignores the LOS warning from the optical transceiver 1 (refer to FIG. Figure 7(d)).

During this period, the optical transceiver 1 outputs an LOS alarm when the received optical power of the optical input signal is lower than the LOS threshold of the received optical power ( FIG. 7( c )). In addition, the data processing unit 3 repeatedly calculates the BER, and when the BER becomes IE-6, determines the reception state to be at the SD level, and records the information. Furthermore, the LOS control unit 4 detects the LOL alarm from the clock/data recovery unit 2 near the BER of IE-4 ( FIG. 7( d )).

Therefore, when the LOS alarm is detected, the LOS control unit 4 outputs the currently existing LOS alarm from the optical transceiver 1 or the detected LOS alarm as an LOS alarm to the data processing unit 3 ( FIG. 7( e )). The data processing unit 3 receives this warning and starts severe failure processing (SF). In this way, according to this example, in the state in which the received optical power drop alarm has been output, the sequence of occurrence of SD and SF is reliably guaranteed.

8 to 10 are diagrams showing a second embodiment of the light input interruption detecting device of the present invention.

The difference between the first embodiment of FIG. 3 and FIG. 8 is that in FIG. 3 , the LOL alarm output from the PLL circuit of the clock/data recovery unit 2 is output to the LOS control unit 4. In contrast, in this example, The data processing unit 3 obtains the BER level IE-4 equivalent to the LOL alarm in FIG. 3 through software calculation similarly to the SD, and outputs it to the LOS control unit 4 as a bit error alarm instead of the LOL alarm. . Other than that, it is the same as the first embodiment.

Therefore, in Fig. 9 and Fig. 10 showing the operation example of the second embodiment, Fig. 9(d) is changed to the bit error alarm of the data processing part, and Fig. 10(d) is also changed to the bit error alarm of the data processing part. Bit error warning. Other than that, it is the same as FIG. 6 and FIG. 7 of the first embodiment. Therefore, for the second embodiment of the present invention, in order to avoid repeated description with the first embodiment, no further description will be given.

As above, according to the present invention, when the optical input power is greater than or equal to the minimum receiving level, the optical input interruption (LOS) can be generated immediately, and when the optical input power is less than or equal to the minimum receiving level, the optical input interruption (LOS) can be generated in the order from SD to LOS .

Claims (7)

1. checkout gear is interrupted in a light input, it is characterized in that, this light input is interrupted checkout gear and had:

The light input part, its basis is to the instrumentation of the received optical power of light input signal, this light input part carries out instrumentation to the received optical power of light input signal, when this received optical power is exported received optical power decline information when the received optical power falling-threshold value is following, when alarm is interrupted in output light input when light input interruption alarm threshold is following, wherein, this light input is interrupted alarm threshold less than this received optical power falling-threshold value;

Synchronous portion, its extraction is contained in the synchronised clock in the above-mentioned light input signal, output step-out alarm when step-out;

Test section is interrupted in the light input, it judges having or not of above-mentioned received optical power decline information, under the situation that has this received optical power decline information, output by above-mentioned step-out alarm makes above-mentioned light input interrupt alarm effectively, under the situation that does not have received optical power decline information, it is effective to make above-mentioned light input interrupt alarm immediately, interrupts alarm according to this effective light input and detects light input interruption; And

Bit error rate instrumentation portion, the bit error rate of the reception data that this bit error rate instrumentation portion recovers using above-mentioned synchronised clock carries out instrumentation, when this bit error rate that measures when predetermined bit error rate value is above, be judged to be other malfunction of minor failure level.

2. checkout gear is interrupted in light input according to claim 1, it is characterized in that, the input of above-mentioned light is interrupted test section under the above-mentioned situation that has received optical power decline information, replacement makes above-mentioned light input interrupt alarm effectively according to above-mentioned step-out alarm output, interrupts alarm and above-mentioned step-out alarm output is considered as effective light input.

3. checkout gear is interrupted in light input according to claim 1, it is characterized in that the bit error rate value of above-mentioned other malfunction of minor failure level is less than the bit error rate value of the malfunction of light input interrupt levels or the bit error rate value of other malfunction of step-out level.

4. checkout gear is interrupted in light input according to claim 3, it is characterized in that the bit error rate value of the malfunction of above-mentioned light input interrupt levels or the bit error rate value of above-mentioned other malfunction of step-out level equal the bit error rate value of other malfunction of severe failure level in fact.

5. checkout gear is interrupted in light input according to claim 1 and 2, it is characterized in that, above-mentioned received optical power decline information is exported by each predetermined period or begun process from the moment of obtaining this information and exports after predetermined time of delay.

6. a light transmitting device is characterized in that, this light transmitting device is by constituting with the lower part:

Optical transceiver, it carries out the transmission and the reception of light signal, this optical transceiver comprises the light input part, this light input part carries out instrumentation to the received optical power of light input signal, when this received optical power is exported received optical power decline information when the received optical power falling-threshold value is following, interrupt alarm when output light input when light input interruption alarm threshold is following, wherein, the input of this light is interrupted alarm threshold less than this received optical power falling-threshold value;

Clock/data recovery portion, its reception data synchronization that is contained in the above-mentioned light input signal is recovered, this clock/data recovery portion comprises synchronous portion, and this synchronous portion extracts the synchronised clock that is contained in the above-mentioned light input signal, output step-out alarm when step-out;

Light input interruption controls portion, it judges having or not of above-mentioned received optical power decline information, when having this information, output by above-mentioned step-out alarm makes above-mentioned light input interrupt alarm effectively, perhaps above-mentioned step-out alarm can be considered as effective light input and interrupt alarm, when this information not, immediately alarm is interrupted in above-mentioned light input and being made as effectively; And

Data processing division, it carries out the processing of above-mentioned reception data, this data processing division comprises bit error rate instrumentation portion, this bit error rate instrumentation portion uses above-mentioned synchronised clock that the bit error rate of the reception data recovered is carried out instrumentation, when this bit error rate that measures when predetermined bit error rate value is above, be judged to be other malfunction of minor failure level, and write down this malfunction, and this data processing division interrupts alarm according to above-mentioned effective light input carries out the troubleshooting that the light input is interrupted.

7. a light transmitting device is characterized in that, this light transmitting device is by constituting with the lower part:

Optical transceiver, it carries out the transmission and the reception of light signal, this optical transceiver comprises the light input part, this light input part carries out instrumentation to the received optical power of light input signal, when this received optical power is exported received optical power decline information when the received optical power falling-threshold value is following, interrupt alarm when output light input when light input interruption alarm threshold is following, wherein, the input of this light is interrupted alarm threshold less than this received optical power falling-threshold value;

Light input interruption controls portion, it judges having or not of above-mentioned received optical power decline information, when having this received optical power decline information, by position error code alarm output, make above-mentioned light input interrupt alarm effectively, when this received optical power decline information not, make above-mentioned light input interrupt alarm effectively immediately; And

Data processing division, it is contained in the processing of the reception data in the above-mentioned light signal, its bit error rate to above-mentioned reception data carries out instrumentation, when bit error rate value that this measures in the 1st bit error rate value with than the 1st bit error rate value between big the 2nd bit error rate value time, be judged to be other malfunction of minor failure level and write down this malfunction, when above-mentioned the 2nd bit error rate value is above, export the alarm of rheme error code in the bit error rate value that this measures, and carry out the troubleshooting that the light input is interrupted according to above-mentioned effective light input interruption alarm.

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